The control system in present auto tuned combiners works independently for each resonator module (channel), the phase is measured in each resonator module and the position of the tuning mechanism is adjusted accordingly. In U.S. Pat. No. 6,041,083, by Larsson et al., the processing is done in one control unit, switching between channels, but the measured data and response is for one channel at a time, see FIG. 1.
The problem with the described control system is that it requires a one-to-one correspondence between the position of the tuning mechanism in a certain resonator module and the measured phase. When resonator modules are coupled in cascade, this one-to-one correspondence is no longer possible to find.
A tunable filter is described in U.S. Pat. No. 6,147,577, by W. W. Cavey, which demands an extremely stable environment to operate properly. The described filter has a built-in fault in that the filter doesn't have any possibilities to adjust it self over time, for instance to compensate for temperature drifts.
In U.S. Pat. No. 5,525,940, by Heikkilā et al., and U.S. Pat. No. 5,638,034, by Heikkilā et al., a device and a method for tuning a combiner filter is disclosed. The technique used is tuning on measurement of mainly reflected power from the resonator module.